Singh Anoop Kumar, Huang Shiau-Yuan, Chen Po-Wei, Chiang Jung-Lung, Wuu Dong-Sing
Department of Materials Science and Engineering, National Chung Hsing University, Taichung 40227, Taiwan.
Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University, Nantou 54561, Taiwan.
Nanomaterials (Basel). 2021 Sep 6;11(9):2316. doi: 10.3390/nano11092316.
Spinel ZnGaO films were grown on c-plane sapphire substrates at the substrate temperature of 400 °C by radio-frequency magnetron sputtering. Post thermal annealing was employed at the annealing temperature of 700 °C in order to enhance their crystal quality. The effect of thermal annealing on the microstructural and optoelectronic properties of ZnGaO films was systematically investigated in various ambiences, such as air, nitrogen, and oxygen. The X-ray diffraction patterns of annealed ZnGaO films showed the crystalline structure to have (111) crystallographic planes. Transmission electron micrographs verified that ZnGaO film annealed under air ambience possesses a quasi-single-crystalline structure. This ZnGaO film annealed under air ambience exhibited a smooth surface, an excellent average transmittance above 82% in the visible region, and a wide bandgap of 5.05 eV. The oxygen vacancies under different annealing ambiences were revealed a substantial impact on the material and photodetector characteristics by X-ray photoelectron spectrum investigations. ZnGaO film exhibits optimal performance as a metal-semiconductor-metal photodetector when annealed under air ambience. Under these conditions, ZnGaO film exhibits a higher photo/dark current ratio of ~10 order, as well as a high responsivity of 2.53 A/W at the bias of 5 V under an incident optical light of 240 nm. These results demonstrate that quasi-single-crystalline ZnGaO films have significant potential in deep-ultraviolet applications.
通过射频磁控溅射在400℃的衬底温度下在c面蓝宝石衬底上生长尖晶石ZnGaO薄膜。为了提高其晶体质量，在700℃的退火温度下进行了后热退火。系统研究了在空气、氮气和氧气等各种气氛中热退火对ZnGaO薄膜微观结构和光电性能的影响。退火后的ZnGaO薄膜的X射线衍射图谱显示其晶体结构具有(111)晶面。透射电子显微镜照片证实，在空气气氛下退火的ZnGaO薄膜具有准单晶结构。在空气气氛下退火的这种ZnGaO薄膜表面光滑，在可见光区域的平均透过率高于82%，带隙为5.05 eV。通过X射线光电子能谱研究发现，不同退火气氛下的氧空位对材料和光电探测器特性有重大影响。当在空气气氛下退火时，ZnGaO薄膜作为金属-半导体-金属光电探测器表现出最佳性能。在这些条件下，ZnGaO薄膜在240 nm的入射光下，在5 V偏压下表现出约10个数量级的更高的光/暗电流比以及2.53 A/W的高响应度。这些结果表明，准单晶ZnGaO薄膜在深紫外应用中具有巨大潜力。
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